This invention relates to a circuit breaker having blow open contacts and more particularly to a magnetic carrier arrangement for reinforcing blow open force.
A current interrupting mechanism called a blow open mechanism is commonly used to handle massive overcurrent conditions to instantaneously open during the first milliseconds that a massive overcurrent condition exists. It is important that the contacts open quickly to interrupt the high current and to prevent the build-up of heat in the circuit breaker. Because of present efforts to reduce the physical dimensions of circuit breakers and other electrical equipment, circuit breaker mechanisms have been made compact; yet, increased performance has been demanded of these breakers. With this reduction in space, there has been an increased need to open the contacts rapidly upon the occurrence of the massive overcurrent condition to prevent damage to the circuit breaker.
Typically, the blow open force is supplied by arranging the contact arms of the blow open assembly so that the current flowing through the fixed contact arm goes along a path which sets up a magnetic field which is opposite to the magnetic field set-up in the movable contact arm. The opposing magnetic fields produce the force to blow the contacts apart. Naturally, the strength of the magnetic field can be influenced by the length and spacing of the contact arms. If space were not a limiting factor, the contact arms could simply be made longer to get a greater blow open effect for a fault current condition. But space is a limiting factor and other means are necessary to derive sufficient blow open force. Accordingly, it will be appreciated that it would be highly desirable to provide a way to increase the magnetic blow open force in the given space.
Accordingly, it is an object of the present invention to provide a contact arm assembly which reinforces the magnetic blow open forces for faster opening upon the occurrence of a fault.
Another object of the invention is to provide a blow open contact assembly which does not increase the physical dimensions of the circuit breaker.